Manufacture of organolead compounds



Patented Nov. 4, 1958 2,859,229 MANUFACTURE OF ORGAN OLEAD COIVIPOUNDS Sidney M. Blitzer and Tillmon H. Pearson, Baton Rouge, La., assignors to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application March 28, 1955 Serial No. 497,379

' Claims. 01460-437 This invention relates to a process for the manufacture of organolead compounds. In particular, this invention is directed to an improved process for the manufacture of tetraethyllead.

The process employed in the present commercial practice for the manufacture of tetraethyllead has been in use for a number of years and, in general, is satisfactory. However, it has certain disadvantages which are overcome by practicing our invention. It proceeds by reacting a sodium-lead alloy, of composition controlled to correspond substantially to NaPb, with ethyl chloride according to the following equation:

With the highest yields obtained thereby, only about 22 percent of the lead present in the NaPb alloy is converted to tetraethylleadf Under conditions of best operation of this process, no one heretofore, as far as we are aware, has been able to increase this yield of tetraethyllead by even a few percent, due to the inherent limitation in yield as is apparent from the consideration of the above equation. It should be noted that in this reaction at least 75 percent of the lead originally employed is not alkylated. Thus, in this reaction, large quantities of lead must be recovered and reprocessed to NaPb alloy in order to make it economical. A further disadvantage of such a large quantity of unreacted lead is that valuable reaction space in the reaction vessel is occupied by materials which are essentially inert for the manufacture of tetraethyllead under present conditions and mode of operation.

' Other processes for the production of organolead compounds and in particular tetraethyllead, have been devised to consume the lead produced in the above equation. While such processes are satisfactory from the standpoint of lead consumption, they suffer an additional drawback in common with the present commercial process in that they require organo halide as the ethylating agent. One such process is that described in U. S. Patent 2,535,190 wherein lead, as for example that produced in the commercial process, is treated with metallic magnesium and ethyl chloride in the presence of a catalyst, preferably an alkyl ether. Thus, in this process as well as the present commercial process, the tetraethyllead manufacturing operation is restricted by the necessary balance between the metallic sodium required and the organic chlorine in the ethyl chloride. t

It is therefore an object of this invention to provide a process for the manufacture or organolead compounds which overcomes the above objections to the present commercial process and those processes which have been proposed morerecently as an improvement thereover. Particularly, it is an object of the invention to increase the conversion of lead to tetraethyllead above that obtained in present commercial practice without requiring the use of metallic sodium, metallic lead, or alkyl halogen compounds.

vThese and other objects of this invention are accomplished by reacting a lead halidewith an organo comalkyl or tetraaryl; lithium, sodium or potassium galliumv tetraalkyl or tetraaryl; lithium, sodium or potassium indi um tetraalkyl or tetraaryl. For convenience these compounds are referred to as tetrahydrocarbo iII-A .alkali metals. o T

In accordance with this inventiomit has been discovered that to produce organolead compounds it is unneces-. sary to start with a lead alloy, orin fact to employ metallic lead at all. employed in the process of this invention is a halide of lead wherein the halogen has an atomic weight greater than 35, namely the chlorides, bromides, and iodides of lead.

The process of the present invention can best be understood by considering the chemical equation involved.. In

where R is an organic radical, A is an alkali metal 'selected from the group consisting of lithium, potassium, and sodium; M is a group III-A metal selected from the group consisting of boron, gallium, aliuminum, and indium; and Y is a halide having an atomic weight greater than 35, that is chlorine, bromine and iodine. In the preferred embodiment of this process the organic radicals are alkyl hydrocarbons or aryl substituted alkyl groups. In general, we prefer the lower alkyl radicals having up to about eight carbon atoms. Among the aromatic radicals which can be employed in the above reaction are included phenyl and hydrocarbon substituted phenyl radicals such as the aralkyl radicals. Thus, the compounds AMR may be considered alkylating agents With respect to the lead in the inorganic lead compound represented by PbY v Of'greatest current importance from a commercial standpoint is the manufacture of tetraethyllead by'the process of this invention. This embodiment can be illustrated by reference to the following equation representing the preferred embodiment.

' Illustrative of the alkylating agents which we can employ are sodium aluminum tetramethyl, sodium boron tetramethyl, sodium gallium tetramethyl, sodium indium tetramethyl, lithium aluminum tetraethyl, lithium boron tetraethyl, lithium gallium tetraethyl, lithium indium tetraethyl, potassium aluminum tetra (2-phenethyl), potassium boron tetra (Z-phenethyl), potassium gallium tetra (2-phenethyl), potassium indium tetra (2-phenethyl), lithium aluminum tetraamyl, lithium boron tetraamyl, lithium gallium tetraamyl, lithium indium tetraamyl, lithium aluminum tetraoctyl, lithium boron tetraoctyl, lithium gallium tetraoctyl, lithium indiumtetraoctyl, potassium aluminum tetrahexyl, potassium boron tetrahexyl, 'potassiurngallium tetrahexyl, potassium indium tetrahexyl and isomeric derivatives thereof and the like. Likewise, the tetrahydrocarbo III-A alkali metals can contain a mixture of alkyl radicals and when these are employed, mixed lead alkyls are produced. V

By the process of this invention, as much as 50 percent of the lead inthe foregoing lead salts is directly converted to organo-lead or in particular, in a commercial embodiment to tetraethyllead. The remaining portion A satisfactory form of the lead to be i versely, the lead so produced by this invention can b recycled economically to the present process by conversion to the appropriate lead.salt.

Our invention is adaptable to the production of-organoleadcompounds. generally, such astetraethyllead,

tetramethyllead, dimethyldiethyllead, tetrapropyllead,

te rahexyllead, tetraarnyllead, tetraoctyllead, and thealkali metals are intended to. be inferred therein.

Ingen'eral, we. contemplate two methods for conducting the process of this invention. One, an alkali metal group. III-A hydride is reacted with an appropriate olefin and a'lead salt to forrnin one stage the desired organo lead compound and the by-product alkali metal and aluminum salts and metallic lead. In a second embodiment we employ in a-second stage alkali metal group III-A tetrahyglrocarbon. along with a lead salt, said hydrocarbon compound having previously been prepared by reaction of. the alkali metal group III-A hydride with an appropriate olefin. In both instances the group. III-A compound is prepared by known methods. For example, lithium aluminum tetrahydridecan be preparedby reacting lithium hydride with aluminum chloride and separating the thus produced by-product lithium chloride. For thepurposes of this invention, however, it is not essential to remove the lithium chloride. as it is essentially: inert in the organo lead reaction. In the other embodiment, we first prepare, for example, lithium aluminum 'tetraethyl by reaction of lithium aluminum tetra hydride with ethylene. Forthe other reactants which are employed in different embodiments of this invention, similar conditions apply.

Generally, the process of this invention is conducted as follows. This general description makes reference to alkali aluminum tetraalkyls but other lII-A compounds are handled similarly. Into a reaction vessel, preferably a stirred autoclave, is placed the desired quantities of alkali aluminum tetraalkyl compound suspended or dissolved in an inert liquid carrier such as, for example, a';hydrocarbon of medium boiling range. The appropriatelead salt, for example lead chloride in finely divided form, is introduced through a hopper containing a plug cock into. the autoclave while agitating to create a suspension of the. organo metallo compound in the inert liquid. carrier. The connection tothe hopper is thereupon closedand moderate heat is applied to the reactionvessel While continuing the agitation. Thereupon, an exothermic reaction ensues and upon reaching the desired reaction temperature, cooling is provided through a jacketin the autoclave. In contrast to other processes for the manufacture of tetraethyllead, when this invention is employed it is not necessary to provide expensive and. complex reflux equipment as, by proper choice of thejcarrier liquid, the reaction can be conducted in a closedsystem. Thus, tetraethyllead can be produced without the copresence of ethyl chloride in the closed vessel. This greatly facilitates control of the reaction and preventsthe existence of an otherwise hazardous operation. After completion of the reaction, the organolead.compound produced is in solution in the carrier liquid1and theother products, namely the alkali metal salt and aluminum salt and metallic lead can be removed by filtration. and the or anolead compound removed fromrthesfcarrier by distillation.

Alternatively, anequally satisfactory method of conductingthe process of this invention comprises the formation of the alkylating agent, for example sodium aluminum tetraethyl, in situ in'the reaction vessel. Thus, sodium aluminum hydride and ethylene and the lead salt are all introduced to the reaction vessel along with a liquid carrier. Upon heating the reaction mixture the pressure due to the ethylene. increases until reaction commences. Thereupon the ethylene is consumed and the pressure becomes lessened due to the formation'sioifi sodium aluminum tetraethyl. Thereupon, this last named.

metal. compound reacts with the lead salt to produce tetraethyllead. It is necessary, however, nottopermlt the temperature at the end of the reaction to increase to such an. extent'that the aluminum chloride produced reacts with and decomposes the tetraethyllead. Thus, depending upon the activity of the III-A halide produced and the stability of the organolead compound produced, the temperature must be closely controlled. For the preparation in sit u.of higher alkyl compounds, it is of course not necessary to employ correspondingly high pressures. Thus, with the normally liquid olefins, a low pressurelow temperature reaction can be employed;

While. the above operations were discussed in connection with a batch operation, they can be successi luy. adapted to a continuous process. In addition to apply: ing the above operations to a continuous process, other modifications of a continuous process can be made, such as first-mixingtogether allthe reaction materialsapd, then passing them continuously through a suitable...re ac= tion zone. It has been indicated that the process of the present invention is conducted in the presence of an inert carrier liquid. Hydrocarbons of appropriate boiling pointwith respectto the organolead compound produced:are.-.sati s factory and. can be. chosen so as to provide a-solution of theproduct suitable for. other applications or sothat they can bereadily removed by distillation at a tempera: tureat-which the organolead compound will not -.decom.-,. pose. Other. inert carrier liquids are satisfactory and where the. product is a liquid such as, for eXample,'-in the manufacture oftetraethyllead, the organoleaqLco npound itself can be employed as a..carrier.-liqu id In such an. operation, economies are effected by; obviating the necessity of recovery by other means thjan merely filtrationof the co-produced solids. carrierv liquids comprises the liquid amines and liquid ammonia and ethers. The principal criterionof choice therefore, of a carrier, isthe-physical characteristic) of the organolead compound-produced, and the inertnessl of the liquid to the alkali metalaluminum tetraalkyLand the. aluminum salt product. Certain ofthe .aforementioned. reactant-carriers, while inert tothe. reactants, exhibit abeneficial effect on the reaction whichzmayi be considered catalytic in nature and;contribute .to theease I of reaction-and rapidity of arriving .at.completion:=of the 1 reaction at relatively lower.:temperatures. and-pressures.

In general, when conducting this process in the presence of a liquid carrier as above, the. amount of carrier should be proportioned so as to. provide adequate .heatremoval facilities. In general, the load on the. heat: transfer.

mediumis proportionaltothe concentration or "relative proportion of the reactants-and carrier. In a batch o'p eration. it:is :preferred to. employ the liquid diluen't{ in the proportion of as much as 1,000 parts per part of organo. metallic reactant; In a continuous-operation or in an operation providing the maximum heat transfer medium, a .more concentrated reaction mixture can be employed wherein as little as, equal parts-by weight of carrier and'organo metallic reactant are employed; In

general, it has been found-that a-more concentrated reactionmixture provides a rapid reaction and, provided adequate heat removal means are'provided, this is; an

advantage as the organolead product is subjected to the elevated reaction temperature for the shortest practical time thereby minimizing I thermal decomposition. 0!. undesirable side -reactions.- i

Another. class; of

This invention can be further understood by the following detailed working example of one method of practicing this invention as directed to the manufacture of tetraethyllead.

Example I Lithium aluminum hydride, 1% parts, under hexane is pulverized and then washed into the reactor to result in a total n-hexane content of 330 parts.. The reactor was flushed with nitrogen, sealed, and then pressurized to 390 pounds per square inch gage with'ethylene. It was then heated to a temperature between about 98 and 102 C. and maintained at this temperature for 5 /2 hours. The reactor was then cooled to room temperature, flushed with nitrogen, then 22 parts of finely divided lead chloride was added thereto. The reactor was again sealed and maintained at a temperature between 20 and 22 C. for 4 .6 hours. At the end of this period the reaction mixture was cooled to room temperature and the pressure in the system was released. Suflicient isopropyl alcohol was added to destroy excess lithium aluminum tetraethyl. The reaction mixture was then filtered to remove solids, then the filtrate was washed with an equal volume of water. The organic layer was transferred to the still for the removal by vacuum distillation of the nhexane. The conversion of lead chloride to tetraethyllead was high, producing an almost quantitative yield of tetraethyllead.

Likewise, the hydrides of sodium and boron, sodium or lithium and gallium, and sodium, lithium, or potassium with indium and other alkali metal group IIIA hydrides can be employed in the foregoing example to react with ethylene and lead chloride to produce tetraethyllead in high yield and purity.

Similarly, when lithium aluminum hybride is reacted with the lead salt in the presence of propylene, and butylene, satisfactory yields of tetrapropyllead and tetrabutyllead are produced.

In general, the reaction of this process is completed Within a relatively short period at elevated temperatures, but a somewhat longer time is required at lower temperatures. In general, a reaction time of between about one-half to twenty hours is employed. In particular, in the manufacture of tetraethyllead with sodium ethyl and lead sulfide, we prefer to employ a reaction time of about ten hours or less.

The pressure employed in the reaction vessel is not critical and is usually the autogenous pressure created by the carrier liquid or the olefin at the temperature employed. Since organo-lead compounds are relatively toxic, it is desirable to employ a closed vessel in conducting this reaction Which may create an elevated pressure if low boiling carrier liquids are employed.

The temperature required to initiate the self-sustaining reaction of this invention varies with the organolead compound being produced. In general, with the lower a'lkyllead compounds such as tetraethyllead, it is preferred to employ temperatures in the range of 25 to 150 C. With aryllead compounds, for example tetraphenyllead, it is preferred to operate in the range of 50 to 150 C.

When the reactants in this invention are both solids, and a solvent therefore is not employed, it is preferred in order to provide a relatively rapid and controllable reaction to employ the reactants in finely divided form, or at least in the form of small granules.

While it was indicated above that in general a catalyst is not required for the practice of this invention, certain materials do exhibit a catalytic eflect upon the reaction and, in many instances, their inclusion in the reaction provides a smoother operation. Typical of such materials are heavy metal iodides as well as iodine itself, organic iodides, certain ketones such as acetone and methyl ethyl ketone, and ethers and amines as indicated heretofore.

The following detailed examples serve to illustrate additional specific embodiments of the present invention.

I6 However, the invention is not intended to be limited thereto.

Example II The procedure of Example I is employed essentially as described with the exception that the sodium aluminum tetraethyl is reacted with the'lead chloride at to C. with quick cooling to room temperature after onehalf hour reaction period. Tetraethyllead'is obtained in high yield and purity. V

In place of the n-hexane employed in the foregoing example as an inert carrier liquid, equally good results are obtained when pentane, benzene, toluene, xylene, triethyl amine, or diphenyl are employed. In addition to the ingredients specified in the foregoing example, thermal stabilizers may be employed, such. as for example naphthalene and styrene to permit operation of the reaction at still higher temperatures without concomitant decom position of the tetraethyllead so produced.

Example III Again conducting the process essentially as described in Example I, tetraethyllead is prepared in high purity and yield when reacting another batch of lithium aluminum tetraethyl as shown with 27 parts of lead bromide.

Example IV Lithium aluminum tetrahexyl is reacted with lead chloride in essentially stoichiometric amounts at room temperature for four hours as in Example I to produce tetrahexyllead in high yield.

The procedure of Example IV can be employed to produce tetrahexyllead by substituting therein the sodium and potassium compounds of aluminum tetrahexyl.

Example V AMR,

wherein A is an alkali metal, M is a group IIIA metal, and R is a hydrocarbon radical containing up through 8 carbon atoms and selected from the group consisting of alkyl and aryl radicals, with a lead halide of a halogen selected from the group consisting of chlorine, bromine and iodine to form said hydrocarbon lead compound.

2. The process of claim 1 wherein said IIIA alkali metal compound is lithium aluminum tetraethyl and said lead halide is lead chloride.

3. The process of claim 1 wherein said IIIA alkali metal compound is sodium aluminum tetraethyl and said lead halide is lead chloride.

4. The process of claim 1 wherein the reaction is conducted in the presence of an inert liquid carrier at a temperature between about 25 to C.

5. A process for the manufacture of a tetraalkyl lead compound selected from the group consisting of a tetraethyl lead through and including tetraoctyl lead which comprises reacting a group IIIA alkali metal hydride with an olefin corresponding to said alkyl radical and reacting the group IIIA alkali metal compound produced with a lead halide of a halogen selected from the group consisting of chlorine, bromine and iodine to form said alkyllead compound.

6. The process of claim 5 wherein said process is con ducted in one stage by providing a reaction mixture com- {arising said group III-A alkali'metal'hydride,'said olefin, and said lead halide.

7. The process of claim 6 wherein said group III-A alkali metal hydrideis lithium aluminum hydride, said olefin :is ethylene andsaid lead halide is lead chloride.

8. The process of claim 6 wherein said group IHA alkali metal hydride is sodium aluminum hydride, said olefin is ethylene, and said lead halide is lead chloride.

9. The process of claim 6 wherein the reaction is conducted in the presence of an inert liquid carrier at a temperature between about 25 to 150 C.

'10. The process of claim'8 whereinthereaction is conr ducted in the presence -of'-an inert liquid carrierat a temperature between about 25 to 150 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Leeper et al.: Chem. Revs., 54, 108 (1954), citing Austin: I. A. C. S., 54,- 3726 (1932).

Ziegler et al. Mar. '26, 1957 

1. A PROCESS FOR THE MANUFACTURE OF AN HYDROCARBON LEAD COMPOUND WHICH COMPRISES REACTING A III-A ALKALI METAL COMPOUND OF THE GENERAL FORMULA 